The objective of this investigation is to study the effect of hormone on adipose tissue metabolism. Adipocytes are studied, using radioactive phosphorus to mark changes in phosphopeptide metabolism, as monitored by polyacrylamide gel electrophoresis with concomitant radioautography. Using this method on the subcellular fractions from adipocytes, it is possible to show reproducible banding of phosphopeptides. The pattern of these phosphopeptides is modified when the adipocytes are acutely (5 minute exposure) to various hormones, to date insulin and epinephrine. Epinephrine has been shown to modify the radioactivity found in two molecular weight species (of 68,000 and 120,000 Daltons) which are found in the endoplasmic reticulum and soluble portions of the adipocyte. Insulin, in turn, has been shown to augment the same 120,000 molecular weight species, but reversed the increased radioactivity found in the 68,000 molecular weight species. Physiologic correlation to define these bands is underway.